1024 Tool Box/Text String/Regular Expression

Regular Expression

Free online regex tester tool, real-time match preview

Regular Expression

Flags:

Test String

Match Result

No match

Common Patterns

What is a Regular Expression?

A regular expression (regex) is a sequence of characters that defines a search pattern. It is used for string matching, validation, searching, and replacement in virtually every programming language. Regex patterns range from simple literal matches to complex expressions with groups, lookaheads, and backreferences.

How to Use the Regex Tester

Enter your regex pattern in the pattern field and add flags (g for global, i for case-insensitive, m for multiline). Type or paste test text in the input area. Matching results are highlighted in real time. The tool shows match count, captured groups, and match positions.

Common Regex Patterns

The tool includes a cheat sheet of common patterns: email validation, URL matching, phone numbers, IP addresses, dates, and more. Click any pattern to load it into the tester with an example test string.

▶What regex flags should I use?

g (global) finds all matches, not just the first. i (case-insensitive) ignores letter case. m (multiline) makes ^ and $ match line boundaries. s (dotAll) makes . match newlines. Combine flags as needed, like /gim.

▶Why is my regex not matching?

Common issues include forgetting to escape special characters (., *, +, ?, [, ], (, ), {, }, \, ^, $, |), missing the global flag for multiple matches, or using incorrect character class syntax.

▶What is the difference between greedy and lazy quantifiers?

Greedy quantifiers (*, +) match as much as possible. Lazy quantifiers (*?, +?) match as little as possible. For example, <.*> matches an entire HTML string, while <.*?> matches individual tags.

▶Does this tool support lookaheads and lookbehinds?

Yes, this tool uses your browser's JavaScript regex engine, which supports lookahead (?=...), negative lookahead (?!...), and lookbehind (?<=...) in modern browsers.

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